1. Field of the Invention
This invention relates generally to improvements in power transmission apparatus, and more particularly, but not by way of limitation, to power transmission apparatus employing chain sprockets or gears.
2. Description of the Prior Art
It is well known in the construction of motorcycles to employ a driving and driven sprocket interconnected by an endless chain to provide power transmission from an engine to the driven wheel. The conventional materials employed in the construction of both driven and driving sprockets in motorcycles, and other vehicles, are metallic in nature and include steel, stainless steel, aluminum and various combinations thereof to provide composite sprocket structures.
Many problems are encountered with the use of chain-sprocket drives on motorcycles and other vehicles. Sprocket and chain wear is excessive because of lubrication difficulty in an environment open to all elements including rain, dust, sand, snow and sunlight. Such accelerated wear occurs because the drive chain and sprockets are made of steel and cannot absorb the energy of impact when the vehicle clutch is engaged suddenly. The teeth of the sprockets tend to be bent out of shape in the direction of force applied by the chain. The sprockets, being constructed of steel or other metal, cannot recover their original shape. Similarly, these forces, when applied to the chain, cause the steel links thereof to be stretched beyond their elastic limit. These factors create a difference in pitch between the constant center-to-center distance of the sprocket teeth and the ever enlarging center-to-center distance between the rollers of the chain.
Attempts are constantly being made to lower the noise levels generated in metal to metal chain and gear drive units. One known prior art means of reducing noise involves the machining or molding of the rear ring or large sprocket of a motorcycle of a synthetic resin material such as nylon. This structure results in lower noise, longer wear and reduced lubrication needs.
A steel roller chain running on steel tooth sprockets requires frequent lubrication with oil to prevent heat buildup, rust and corrosion. Such lubrication presents three distinct undesirable effects. The lubricant tends to be thrown off the chain when the vehicle is moving leaving the chain and sprockets vulnerable to water and snow allowing rust and corrosion to occur. As the lubricant is thrown from the moving chain, it is ordinarily deposited on the rear wheel or tire of the vehicle and often on the person or clothing of the rider. Additionally, the existence of lubricating oil on the chain attracts and retains dirt, sand, and other abrasive materials on the rollers of the chain and the teeth of the sprockets where these materials will cause the most wear.
The prior art steel sprocket and chain units are by their nature relatively heavy, requiring additional engine power to turn them. Unnecessary added weight, particularly in the sprocket and chain units, increases the polar moment of inertia of the sprockets and decreases the power to weight ratio of a motorcycle thereby decreasing the performance potential of the vehicle.
Steel chain and sprocket drive mechanisms exhibit relatively high friction and heat generation characteristics especially when there is a breakdown in lubrication as mentioned above. Such heat generation, which is occasioned by the relatively high coefficient of friction between two steel members, results in undesirable power loss in the operation of the motorcycle or other device employing such a power transfer mechanism.
Due to differences in rear wheel designs and spline designs on the power output shafts of various motorcycles produced by different motorcycle manufacturers, it is generally necessary to purchase an entirely different front or counter sprocket and/or rear sprocket to change the gear ratio between the transmission output shaft speed of the driven rear wheel. Ratio changes are desirable because of varied uses to which a motorcycle might be put such as road racing, highway use, moto cross, Enduro, flat track, hill climbing or trail riding.
Efforts have been made in the past to design a suitable driving or counter sprocket for use on motorcycles constructed of synthetic resin materials such as nylon or Delrin. While the toothed portion of the sprockets have been found capable of transmitting sufficient power from the transmission output shaft to the chain, the spline connections between the hub portions of such synthetic resin sprockets and the transmission power output shafts have not proved reliable in transmitting such power from the shaft to the sprocket. Thus, the motorcycle industry has been forced to continue utilizing steel or other suitable metals to construct the entire driving sprocket.